The invention relates to an electrical apparatus which is used, in particular, for receiving signals or outputting signals. The electrical apparatus can be, in particular, a fire alarm or a signal transmitter for an optical indicator, for example for indicating an emergency exit.
Electrical apparatuses of this kind are intended to be mounted on a substrate, for example a ceiling or a side wall. The electrical apparatus points to a base which is attached to the substrate, and a functional head which is reversibly mounted on the base. The functional head can have, for example, a smoke detector for detecting smoke, in order to identify a fire. When in the form of a signal transmitter, a lamp or a lighting means, for example, is provided in the functional head.
DE 198 08 872 A1 describes an alarm of this kind. The base is used for connecting electrical lines. A bayonet connection for locking and contact-making purposes is formed between the base and the alarm head.
Alarms of this kind are sometimes fitted relatively high up, and therefore they generally cannot be replaced by a user when he is standing up. To this end, auxiliary apparatuses are sometimes used, in particular so-called “picker rods”, which allow the functional head to be grasped and removed by said functional head being rotated and pulled out of the bayonet connection.
However, disadvantages or problems sometimes occur in this case. For example, when the apparatus is fitted on an uneven substrate, there may be an insufficient degree of contact reliability in the event of deformation of the alarm head. Handling by means of, for example, picker rods may lead to a relatively high force effect if not applied with an accurate fit, and this may possibly bend or damage sensitive parts. This may, in particular, also damage the electrical contacts. By forming the electrical contacts in the bayonet connection, said electrical contacts are subject to loading by the axial displacement and subsequent relative displacement, even when the bayonet connection is properly formed, if the user executes the movements with force.
In this context, a bayonet connection or a bayonet fitting is understood to be, in particular, a connection between two components in which the two components are connected by axial adjustment, in particular axial insertion one into the other, and subsequent relative rotation. During the axial adjustment, a projecting part, which can be designated a lug in general, is displaced in the axial direction in a corresponding recess; during the subsequent relative rotation of the two components, the projecting part slides in a slot which adjoins the recess (or is in the form of part of the recess) in a peripheral direction.
Bayonet connections are generally secured by clamping; to this end, systems with spring tension in the axial direction and systems with a frictional connection, for example, are known.
Furthermore, apparatuses of this kind which are fitted to a wall or ceiling are subject to shaking and vibrations which may lead to the contact-making means becoming loose and possibly to the bayonet connection becoming unlocked.
Secure bayonet connections can sometimes be formed by relatively complex designs with a relatively high number of parts used. However, this produces costly solutions having a plurality of manufacturing steps and a high degree of outlay on installation. In particular, certain mounting tolerances have to be complied with, depending on the construction, so that secure contact is ensured even when used at a relatively high level.